In recent years, a mobile telephone has been put into widespread use. Various types of mobile telephones have been developed.
Among the various types of mobile telephones, attention is focused on a folding mobile telephone whose upper and lower cabinets can be folded when the mobile telephone is carried or is not used, a compact slide type mobile telephone with portability enhanced as upper and lower cabinets are slid, a compact rotary mobile telephone with portability enhanced as upper and lower cabinets are rotated, and the like from the viewpoint of ease of use considering the portability, etc.
The folding mobile telephone, the slide type mobile telephone, and the rotary mobile telephone have each a structure to allow the mode or the form to be changed in response to the use state and therefore it is important to secure the antenna characteristic in the mode or the form.
The folding mobile telephone, the slide type mobile telephone, and the rotary mobile telephone are furthermore miniaturized and made multifunctional and particularly incorporating of an antenna to improve design is proceeding as one of the multiple functions (for example, patent documents 1 and 2).
The following first to third methods are known as a method of securing the antenna performance in both a conversation mode (at the extension time) and a portable mode (at the housing time) in the folding mobile telephone, the slide type mobile telephone, and the rotary mobile telephone:
The first method is a method of attaching an antenna to the upper end outside of an upper cabinet with the antenna exposed; this method has the following advantage:
Usually, a mobile telephone includes a liquid crystal display element (LCD) on an upper cabinet and thus when the mobile telephone is housed, the upper cabinet is positioned on the top of a lower cabinet. Therefore, if the housed mobile telephone is put on a metal substance, the upper cabinet is brought away from the metal substance.
Thus, the antenna is attached to the upper end part of the upper cabinet, so that the antenna can be brought away from the metal substance and if the mobile telephone is put on the metal substance, the antenna characteristic can be kept good.
On the other hand, the first method has the following disadvantage:
Since a face is brought close to the antenna during telephone conversation, it is difficult to suppress the specific absorption ratio (SAR) representing the average energy amount of radio waves to the reference value and the appearance is impaired because of projecting the antenna and placing slantingly, etc., to bring the antenna away from the face and the method runs counter to recent antenna incorporating.
Usually, the mobile telephone has a battery housed in the lower cabinet and therefore a wireless section is also housed in the lower cabinet. Thus, power needs to be supplied to the antenna of the upper cabinet using a coaxial line, etc., and the wiring and a break caused by bending the line introduce a problem, causing an increase in costs.
Further, in the incorporating method, when the mobile telephone is extended, the physical size of the antenna is small and thus the antenna characteristic is poor.
The second method is a method of attaching an antenna to the upper end outside of a lower cabinet with the antenna exposed; this method has the following advantage:
Since the antenna can be placed at a position distant from a face during telephone conversation, it is advantageous for securing the SAR and in the extension state, the antenna becomes a resonant element for exciting an upper cabinet and the whole mobile radio apparatus operates with the upper cabinet and the lower cabinet as a radiating element and a wide-band characteristic can be provided.
Since power can be supplied to the antenna with spring contacts from a wireless board existing in the lower cabinet, a coaxial line, etc., becomes unnecessary and simplification is made possible.
On the other hand, the second method has the following disadvantage:
Since electric current concentrates on the antenna as the radiating element, the effect of a hand and a face is large during telephone conversation and the characteristic at the telephone conversation time fluctuates largely.
When the mobile telephone is put on a metal substance, the antenna is brought close to the metal substance and it is difficult to keep the antenna characteristic good.
The third method is a method of using the board (circuit board) in a cabinet as an antenna; this method has the following advantage:
The circuit board in the cabinet is used as the antenna, so that the upper and lower circuit boards operate as a dipole antenna and the effective area of the antenna is provided large, so that a wide band and a high gain are made possible.
Since electric current does not concentrate on some elements, the effect of a hand and a face is small.
In addition, the third method is excellent in design and is preferred because it is not necessary to attach the antenna to the outside of the cabinet with the antenna exposed.    Patent document 1: JP-A-2002-335180    Patent document 2: JP-A-2001-156898